Catalyst for oxidation of olefins

ABSTRACT

A process for the oxidation of olefins to the corresponding unsaturated aldehydes and acids, e.g. propylene to acrolein and acrylic acid, by reacting the olefin with oxygen in the presence of a catalyst of the empirical formula

Umted States Patent 1 1 [11] 3,875,078 Levy 5] Apr. 1, 1975 {5 CATALYSTFOR OXIDATION OF OLEFINS 3,451,946 6/1969 Ziegler et al 252/4393,578,707 5/1971 Bethell et a1 260/533 N X [75] Inventor: Levy CorpusChm", 3,64 ,138 2/1972 Ondrey et al. 252/439 [73] A i CelaneseCorporation, New York, 3,655,747 4/1972 Sennewald et a1 252/470 X N Y3,655,749 4/1972 Ondrey et a1. 252/439 X 3,655,750 4/1972 Ondrey et a1.252/439 X [22] Filed: May 24, 1973 3,668,147 6/1972 Yoshino et a1252/439 X [2]] Appl' 363450 Primary Examiner-H. Sneed Related U.S.Application Data Attorney, Agent, or FirmStewart N. Rice; Ralph M. [62]Division OfSer. NO. 225,536, Feb. 15, 1972, Pat. NO. Pmche" [57]ABSTRACT [52] U.S. Cl. 252/432 A process for the oxidation of olefins tothe corre- [51] Int. Cl BOlj 11/82 sponding unsaturated aldehydes andacids, e.g. propyl l Field of Search 0; lene to acrolein and acrylicacid, by reacting the olefin 260/533 N with oxygen in the presence of acatalyst of the empirical formula [56] I References Cited MoucobTecxdopUN TED STATES PATENTS wherein X is rhodium or boron. When a is 100, b is3.098.102 7/1963 Bcthell ct ul 260/533 N X 4 0 20O C is O.1 7 0 and d is5 7 when X is rhodium 3.240806 3/1966 Bethell ct al..... 252/439 X3.271.447 9 1966 NaylOl' 252/470 x and to when X boron 3.347.899 10/1967Caporali et al. 252/439 X 6 Claims, N0 Drawings CATALYST FOR OXIDATIONOF ()LEFINS This is a division of application Ser. No. 225,536, filedFeb. 15, 1972.

BACKGROUND OF THE INVENTION The present invention relates to a methodfor the oxidation of olefins to the corresponding unsaturated aldehydesand unsaturated carboxylic acids, and to a catalyst therefor.

Numerous methods are known in the prior art for the oxidation of olefinsto oxygenated products such as unsaturated aldchydes and acids. Forexample propylene may be oxidized to produce acrolein and acrylic acid.Among the catalysts known for effecting such conversions is cobaltmolybdate mixed with tellurium dioxide or tellurium. Even though theseand other catalysts are effective in olefin oxidation processes, theygenerally do not give good selectivity to the desired unsaturatedaldehyde and acid products and many of them also fail to give adequateconversions. As used herein the terms conversion and selectivity aredefined as follows:

Conversion,

moles olefin fed Selectivity, mole moles olefin converted moles ofdesired product moles olefin converted to oxygenated products. When thecatalyst contains boron, that is when the catalyst is of the formulaMo,,Co,,. Te,.B,,O,., it is preferred that the elements of the catalystbe present in atomic ratios such that when a is I00, h is 50-150, c is0.2-5.0, d is l-50 and e is 350700. However when the catalyst containsrhodium and is thus of the empirical formula Mo,,Co,,Te,.Rh,,O,., theatomic ratio of the elements is preferably such that when a is 100, b is50450, c is 0.2-6.0, d is 015-20, and e is 350700.

The exact structure of the catalysts of the present invention is notknown but they may be considered as a mixture of the oxides of thevarious metals and/or as true compounds ofa coordinate complexstructure. For example the catalyst might be considered as a mixture ofcobalt molybdate with tellurium oxide and either a rhodium or boronoxide. Various methods can be utilized for forming the catalyst whichmay be supported or unsupported. The starting materials may be dryblended or may be combined in the form of aqueous solutions or asaqueous slurries. The dry blending is the 11 ns aturated alde hyde s electivity unsaturated acid selectivity It is thus an object ofthe presentinvention to provide a process for the oxidation of olefins,particularly propylene, which will give high total useful selectivity tothe corresponding unsaturated aldehydes and carboxylic acids, such asacrolein and acrylic acid. It is another objcct ofthe present inventionto provide a novel catalyst composition which may be utilized in anolefin oxidation process.

SUMMARY The present invention in one of its embodiments is a process bywhich an olefin may be oxidized to produce the correspondingethylenically unsaturated aldehyde and carboxylic acid, said processcomprising reacting in the gas phase said olefin with oxygen in thepresence of a catalyst of the empirical formula wherein X is boron orrhodium and wherein the atomic ratio of MozCofIezXzO is such that when ais 100, b is 40-200, is 0. l7.0, dis either -75 when X is boron or 0.l-3.0 when X is rhodium. and v is 300900. In another aspect the presentinvention is said catalyst of the formula DESCRIPTION OF THE PREFERREDEMBODIMENTS least preferable method because of the difficulty inobtaining uniformity throughout the catalyst.

A general method for forming the catalyst is to calcine a solid obtainedby combining cobalt molybdate. a tellurium oxide and a boron or rhodiumcompound, which compound may be an oxide or a compound convertible tothe oxide. Specifically the formation otcatalysts may be accomplished byforming an aqueous solution of a rhodium or boron compound (such asrhodium nitrate, rhodium trichloride or boric acid) and adding theretothe requisite amount of water insoluble tellurium dioxide so as to forma slurry. This slurry is then combined with cobalt molybdate or anaqueous slurry thereof and blended thoroughly. The liquid is thenevaporated from the blend so as to leave a solid which is calcined atabout 200 to 600C. The catalyst is preferably granulated or pelletedbefore use in an oxidation process and this may be accomplished eitherbefore or after calcining. In the foregoing procedure an aqueous slurryof a water-insoluble rhodium or boron compound, such as rhodium oxide orboric oxide, can be utilized instead of the aqueous solution of therhodium trichloride or boric acid. Also a solution of a water solubletellurium compound can be utilized such as an aqueous solution ofammonium tellurate.

If the catalyst is to be supported an aqueous slurry of the support canbe blended with the slurry containing the catalyst components beforeevaporation and calcining. Other methods for loading the catalyst on asupport will also be obvious. Suitable supports include silica. alumina,silicon carbide, alumina-silica, titania, charcoal, clays, and the like.

The cobalt molybdate for use in such catalyst preparations may beobtained in known manner such as by combining a solution of ammoniummolybdate with a solution of a cobalt salt, adding ammonia, and thenfiltering, and drying the precipitate. Preferably the cobalt molybdateis granulated before admixing with the other catalyst components.

The process of the present invention may be carried out continuously ornon-continuously and the catalyst may be present in various forms suchas in fixed beds or as a fluidized system. Portions of the reactants,which do not undergo reaction may be recycled if desired. Where it isdesired to produce an unsaturated acid as the ultimate product, theunsaturated aldehyde produced in the oxidation process may be separatedfrom the effluent and be either recycled to the reaction zone or passedto a second stage oxidation zone.

The temperature utilized in the oxidation process should generally bebetween about 250 to 550C although the exact temperature utilized in aparticular situation will depend largely on the desired productcomposition. When high selectivity to an unsaturated carboxylic acid isdesired then higher temperatures on the order of 350 to 550C willusually be used and when it is desired to increase the selectivity to anunsaturated aldehyde lower temperatures on the order of 250 to 500C willusually be used.

The pressure utilized in the process of the present invention may besubatmospheric, atmospheric or superatmospheric and should be betweenabout 0.5 and 3.0 atmospheres for best results, although pressures ranging up to 7.0 atmospheres and higher may be suitably employed. Thecontact time of the reactants with the catalyst at the reactionconditions should generally be between about 0.1 and seconds but ispreferably a time within the range of 0.5 to 10 seconds. As used hereinthe term contact time refers to the contact time adjusted to C andatmospheric pressure (conditions denoted by NTP). Thus the contact timeis calculated by dividing the volume of the catalyst bed (includingvoids) by the volume per unit time flow rate of the reactants at NTP.

The oxygen necessary as a reactant in the present process may be fromconcentrated molecular oxygen or may be from a more diluteoxygen-containing gas wherein the molecular oxygen is mixed in varyingamounts with an inert diluent gas such as nitrogen, argon, or carbonoxides. For instance air may be utilized the source of oxygen. Theolefin and/or oxygencontaining gas may be separately introduced into thereaction zone at one or a plurality of points along the length of thereaction zone or may be premixed before entering the reaction zone.However the contact of the olefin and the oxygen-containing charge arepreferably kept to a minimum before entering the reaction zone. Thereactants may be pretreated before entering the reaction zone such asfor the removal of undesirable components therefrom.

In conducting the oxidation reaction, the gaseous feed mixture shouldgenerally contain from about 0.5 to 7.0 moles of oxygen per mole of theolefin although the preferable range is from 1.0 to 5.5 moles per mole.Although it is not required, water is also desirably present in thegaseous feed in amounts of from 1.5 to 15, preferably 5.0 to 12 molesper mole of unsaturated hydrocarbon. Care should be taken to avoidcontacting the catalyst with liquid water during operation. In additionto water, diluents which are gaseous under the reaction conditions andare relatively inert may be introduced into the system. Suitablediluents include CO nitrogen and flue gas as well as paraffinichydrocarbons such as are frequently present in commercially- Preparationof Cobalt Molybdate Ammonium molybdate tetrahydrate (353 g) wasdissolved in 400 cc of water containing 165 cc concentrated ammonia. Asolution of 582 g cobalt nitrate hexahydrate in 700 cc water was slowlyadded to the molybdate solution at C. The mixture was allowed to standovernight after which the supernatent liquid was decanted. Theprecipitate was washed three times with 600 cc portions of water. lt wasthen dried at l 10C, the weight of dry material being 421 g.

Preparation of Catalyst A Cobalt molybdate (30.0 g) and 0.15 g oftellurium dioxide were blended together using cc of water as thedispersant. The slurry was evaporated to dryness and the resulting solidcalcined at 400C for 16 hours. The catalyst was comminuted to from 20 to30 mesh, U.S. The catalyst can be represented by the empirical formulass iiio iI.a5 4lir- Preparation of Catalyst 8" Cobalt molybdate (30.0g), 0.15 g rhodium trichloride trihydrate and 0.60 g of telluriumdioxide were blended together using 100 cc water as dispersant. Theslurry was evaporated to dryness and the resulting solid calcined at400C for 16 hours. The catalyst was com minuted to from 20 to 30 mesh,U.S. The catalyst can be represented by the empirical formula Co Mo (l2.6 l).40 -i72- Preparation of Catalyst C" To 29.7 g of Catalyst A wasadded 2.97 g of boric acid and the solids mixed by blending with 100 ccof water. The slurry was evaporated to dryness and the resulting solidcalcined at 400C for 16 hours. The catalyst was comminuted to from 20 to30 mesh, U.S. The catalyst can be represented by the empirical formulaCOMM IUll 0.ti5 1H 5I 8- EXAMPLE 1 Several runs were made in whichrhodium-containing Catalyst B and prior art Catalyst A were utilized forthe conversion of propylene to acrolein and acrylic acid. In all ofthese runs the catalyst was used in a U-tube fixed bed reactor, theU-tube having a total length of about 60 inches. The feed mixtureconsisting of propylene, air and water was premixed and preheated to thereaction temperature prior to introduction into the reactor. Thecomponents of the feed were present in amounts such that the molar ratioof propylenezoxygenzwater was l:3.6:9.4 and the contact time in all theruns was 1.8 seconds (NTP). In order to compare Catalyst A torhodium-containing Catalyst B at similar propylene conversions thetemperature was adjusted in each run to that indicated in the followingtable summarizing the results.

Catalyst B A B A B A Temperature. C 375 350 399 375 448 400 Propyleneconversion, "/1 47 46 79 79 90 95 Acrolein selectivity, mol 71 67 50 4125 30 7 Acrylic acid selectivity. mol 26 35 45 51 38 45 Total usefulselectivity, mol "/1 93 85 86 76 68 52 EXAMPLE H 10 2. A catalystcomposition of claim 1 wherein X is bo- The following table summarizesthe results obtained ron. with boroncontaining Catalyst C. and forcomparison 3. A catalyst composition of claim 2 wherein the ele-Catalyst A at similar propylene conversions. The appaments of saidcatalyst are present in atomic ratios such ratus, feeds and contacttimes were the same as in Exthat when a is 100, b is 50-150, is 0.2-5.0,11 is -50, ample 1. l5 and e is 350-700.

Catalyst C A C A Temperature, C 400 375 425 400 Propylene conversion. Z86 85 95 95 Aci'olein selectivity. mo] 71 11 9 7 Acrylic acidselectivity. mol /1 58 52 51 45 l'ntal uselul selectivity. mol C1 78 6360 52 The embodiments of the invention in which an cxclu- 4. A catalystcomposition of claim 1 wherein X is sive property or privilege isclaimed are defined folrhodium. lows: 5. A catalyst composition of claim4 wherein the ele- 1. A catalyst composition of the empirical formulaments of said catalyst are present in atomic ratios suchMo,,Co,,Te,.X,,O,. wherein X is boron or rhodium and that when a is 100,h is 50-150, 0 is 0.2-6.0, d is wherein the atomic ratio of Mo:Co:Tc:X:Ois such that 0.15-2.0, and e is 350-700.

when u is 100, h is 40-200, 0 is 0.1-7.0, dis either 5-75 6. Thecatalyst composition of claim 1 wherein said when X is boron or 0.1-3.0when X is rhodium, and e catalyst composition is unsupported. is300-900.

1. A CATALYST COMPOSITION OF THE EMPIRICAL FORMULA MOACOBTECXDOE WHEREINX IS BORON OR RHODIUM AND WHEREIN THE ATOMIC RATIO OF MO:CO:TE:X:O ISSUCH THAT WHEN A IS 100, B IS 40-200, C IS 0.1-7.0, D IS EITHER 5-75WHEN X IS BORON OR 0.1-3.0 WHEN X IS RHODIUM, AND E IS 300-900.
 2. Acatalyst composition of claim 1 wherein X is boron.
 3. A catalystcomposition of claim 2 wherein the elements of said catalyst are presentin atomic ratios such that when a is 100, b is 50-150, c is 0.2-5.0, dis 10-50, and e is 350-700.
 4. A catalyst composition of claim 1 whereinX is rhodium.
 5. A catalyst composition of claim 4 wherein the elementsof said catalyst are present in atomic ratios such that when a is 100, bis 50-150, c is 0.2-6.0, d is 0.15-2.0, and e is 350-700.
 6. Thecatalyst composition of claim 1 wherein said catalyst composition isunsupported.